The present invention relates to an improvement in a lead-acid bipolar electrode battery which is constructed in accordance with the process described in copending application for letters patent, Ser. No. 850,290, filed Nov. 10, 1977, and assigned in common with the present application. That copending application, which shall be referred to as the Turillon et al application, discloses novel battery support structures and processes for making such structures. The disclosed processes involve forming a porous matrix of a valve metal or an alloy which exhibits valve metal-like electrical characteristics, impregnating that matrix with lead or a lead alloy and thereafter oxidizing part of the lead to lead dioxide. The Turillon et al application discloses, inter alia, the utility of such lead-impregnated valve metal structures to a bipolar electrode lead-acid battery.
A bipolar electrode lead-acid battery embodying lead-impregnated valve metal support structures can consist of a series of sheet-like electrodes stacked in parallel to one another. The end electrodes of the stack would support respectively positive and negative active mass, whereas the intermediate electrodes would be bipolar each supporting positive active mass on one face and negative active mass on the opposite face. Each of these electrodes might consist simply of a lead-impregnated titanium matrix with the active mass applied to opposite faces thereof, or alternatively the electrode support structure may be a composite consisting in part of a lead-impregnated titanium matrix and in part of a solid mass of metal bonded to that matrix.
Such a battery can be described as a plurality of series-connected cells where each cell is bounded by the positive portion of a bipolar electrode and the negative portion of the adjacent bipolar electrode. The electrolyte, i.e. the battery acid, within each of these cells has to be isolated from the electrolyte in the other cells. This is ensured by an appropriate construction of cell-walls which cooperate with the electrodes to define the individual isolated cell compartments. For the sake of convenience we will describe a battery which is generally cylindrical in shape and features disc-shaped electrodes. It will be understood that the invention is by no means limited to this particular circular configuration. A convenient construction for a cylindrical type of battery involves the use of disc-shaped electrodes and cell-wall members which are tubular and are urged into an electrolyte-tight contact with a respective pair of adjacent electrodes. The seal, which will take place at or near to the disc edges can be a direct cell wall to electrode seal if the cell wall members are of suitable resilience, or alternatively an intermediate sealing device such as an `O` ring may be employed between the cell wall member and the electrode.
When such a bipolar-electrode battey includes electrodes one or both surfaces of which is, for example, a lead-infiltrated titanium matrix, problems have been found to arise in maintaining an electrolyte-tight seal between the electrode and its respective cell wall member. Thus we have found that even if a good seal is present at the time of assembly of the battery, there is a tendency upon use of the battery during a number of charge-discharge cycles for the electrolyte to begin to seep across the seal at various places and hence pass out of its individual cell compartment. This phenomenon, which we refer to as `electrolyte creep`, is observed in particular at the positive face of a bipolar electrode and if unchecked would place a severe limitation on the useful life of the battery.